The present invention relates to a measuring method for continuously measuring, in a non-contact manner, the average particle size of granular material accumulated in a pile by use of image processing.
In the case of a blast furnace or electric furnace, it has been known that there exists a high degree of correlation between the average particle sizes of its raw materials, e.g., sintered ore, cokes and pellets and the furnace operating conditions and the particle size control of these charges has been an essential point for the stable operation of the furnace. In the past, however, there has been no suitable method capable of measuring such particle sizes in a short period of time and in a simple way and therefore the control has been effected by relying on the visual observations of the operator or the sampling measurement of the order of several times a day, thus failing to ensure satisfactory control accuracy.
On the other hand, if the average particle size of such charges can be continuously measured, for example, on a conveyor or on a granulating machine or pelletizer in the case of pellets, the particle size control of the charges can be improved rapidly with the resulting great contribution toward the stable operation of the furnace. From this point of view heretofore much has been expected of the development of a system for measuring the average particle size of granular material accumulated in a pile in a continuous and non-contact manner.
To meet this demand, as disclosed for example in Japanese Laid-Open Patent No. 54-148558, there has been proposed in the past a method of determining the average particle size of granular material accumulated in a pile by televising the granular material with a television camera and processing the resulting image.
In the method disclosed in Japanese Laid-Open Patent No. 54-148558, the charged material being transported by a belt conveyor is illuminated by a flashlight and picked up with a television camera, thereby enhancing the contrast of the image by a video processing equipment. Thereafter, the image enhanced in contrast is applied through a processed image generator to a picture roughness measuring unit which in turn determines the repetition frequency of the light and shade greater in contrast than a given level (corresponding to the average intergranule distance) with respect to the selected scanning lines, and then the light and shade repetition frequency is converted to the average particle size by a computing unit, thereby displaying it on a display unit.
The method disclosed in Japanese Laid-Open Patent No. 54-148558 is a method in which the so-called average inter-granule distance of the granular material shown in the picture is determined to estimate the average particle size. Thus, where the materials to be measured are, for example, the raw materials for steel which are each accumulated in a pile, variations tend to be caused in the measurements and it is difficult to ensure satisfactory measuring accuracy due to the following factors:
1) In the case of sintered ore, coke or pellets under granulation, there are many irregularities in the surface of the granules and they tend to cause the shading which tends to be mistaken for granule-granule boundaries.
2) When accumulated in a pile, the granule-granule boundaries are not clear in many cases and adjacent two granules tend to be mistaken for a single granule.
As described hereinabove, the method of processing the image itself to measure the period of light and shade has tended to suffer the effect of disturbances.